There is tremendous need for smoking cessation intervention technologies with strong potential population-level impact at the lowest possible cost. That potential can be found in the newest technological innovation in quit smoking interventions: smartphone-based smoking cessation software applications (apps). There are over 400 smoking cessation apps, which were downloaded in the United States 3.2 million times during the two-year period 2012 to 2013. No trials of any app's effectiveness for general adult cessation have been published and no NIH-funded cessation intervention trials are in progress-despite the fact this is a high priority NIH funding topic. The enormous usage of smoking cessation apps contrasted with their unknown effectiveness creates a serious scientific gap that could stifle their population-level impact. Research on US Clinical Practice Guidelines (USCPG) apps begins to address that research gap. But only following the USCPG has had limitations in other modalities of delivery. An approach, called Acceptance & Commitment Therapy (ACT), addresses these limitations with both innovative intervention content and highly promising results from six published trials. ACT's innovation is its dual focus on increasing willingness to experience physical cravings, emotions, and thoughts that cue smoking while making values-guided committed behavior changes. We recently developed the first ACT app for smoking cessation, called SmartQuit, and tested it in a pilot randomized controlled trial (N 196), comparing it with an app that follows USCPG (National Cancer Institute's QuitGuide). Results showed that SmartQuit had: (1) higher participant engagement and satisfaction than QuitGuide, (3) higher levels of acceptance of cravings than QuitGuide, and (3) descriptively higher quit rates (albeit non-significant) than QuitGuide at the two-month follow-up. Building on these promising results, we propose a fully-powered three-arm randomized controlled trial (n = 811 per arm) that compares SmartQuit to QuitGuide and each app to the NCI's Clearing the Air booklet, which follows the USCPG, to definitively determine whether (1) an USCPG app is more efficacious than a USCPG self-help booklet; (2) an ACT app is more efficacious than a USCPG booklet; (3) an ACT app is more efficacious than a USCPG app. As millions of people are choosing smartphone apps to help them quit smoking, this innovative study shows exciting promise for improving the success rates of quit smoking apps and thereby lowering healthcare costs and reducing premature tobacco-related deaths.